This invention relates to rechargeable batteries used in energy-using devices. More particularly, this invention relates to rechargeable batteries and an electrical circuit used in energy-using devices which may be covered either by an external source of power or by power from batteries of either the rechargeable or non-rechargeable type and which have built-in charging means for recharging the rechargeable batteries.
Many battery operated consumer products on the market drain energy from the batteries at high rates. Because of these high drain rates, these energy-using devices are particularly suitable for use with rechargeable batteries and, for user convenience, many of these devices have an electrical circuit which, in addition to permitting the device to be operated from both an external source of energy or from the energy supplied by the battery, permits the battery to be charged while it resides in the energy-using device. That is to say the energy-using device has built-in electrical circuitry for charging the rechargeable battery when the energy-using device is connected to a source of external electrical power.
Rechargeable batteries, such as nickel cadmium rechargeable batteries, are sold in the same AA, AAA, C or D sizes as are primary (non-rechargeable) batteries and, accordingly, either rechargeable or non-rechargeable batteries may be inserted into the energy-using device. Thus, a consumer has the choice of operating the energy-using device with either rechargeable or non-rechargeable batteries. It is known to be advantageous, when employing the circuit described above, to include means in the electrical circuit which will preclude a non-rechargeable battery from being charged if the non-rechargeable battery is installed in the energy-using device. Otherwise, the delivery of charging current to the non-rechargeable battery might possibly result in leakage of electrolyte from the non-rechargeable battery and damage to the energy-using device.
U.S. Pat. No. 4,489,268 teaches a rechargeable battery and electrical circuit for charging a rechargeable battery while it is installed in an energy-using device. This patent further teaches a rechargeable battery with a circumferentially extending charging terminal contact, disposed on the cylindrical surface of the battery between the power terminal contacts of the rechargeable battery. The charging terminal contact on the battery engages a charging terminal contact in the electrical circuit of the energy-using device to effect charging of the rechargeable battery. Non-rechargeable batteries not having the charging terminal contact on its cylindrical surface will not engage the charger's charging terminal contact and hence the non-rechargeable battery will not receive charging current from the charging circuit.
The application of the teachings of U.S. Pat. No. 4,489,268 to smaller standard-size rechargeable batteries, such as AA and AAA standard size batteries is not entirely suitable. More specifically, the permissible diameters of these smaller standard-size batteries are defined by industry standards which set, among other parameters, the maximum diameters of the batteries. For nickel cadmium rechargeable batteries in AA and AAA standard sizes the maximum diameter of the battery corresponds to the diameter of the cell container in which the cell electrodes and electrolyte reside. The limitation in maximum diameter imposed by industry standards is necessary in order to permit the consumer to insert the battery in any of the wide variety of energy-using devices in the marketplace designed to operate on that specific standard size battery. Since many of the AA and AAA rechargeable nickel cadmium batteries on the market today have cell container diameters at or near the maximum diameter permitted, application of the teachings of U.S. Pat. No. 4,489,268 would result in a rechargeable battery with a diameter at the charging terminal contact larger than that defined by industry standards. On the other hand, if the diameter of the charging contact on the battery is set at the maximum diameter permitted by industry standards, then the diameter of the cell container will be less than that defined by industry standards. The former is unacceptable since the battery would not fit in at least some consumer products. The latter is disadvantageous because the reduced diameter of the cell container will very likely result in the cell container having a lesser amount of electrochemically active material therewithin. The reduction in the amount of electrochemically active material results in the cell having a shorter run time (or smaller deliverable energy capacity) than a cell having a container diameter at the maximum diameter defined by industry standards. Accordingly, application of the teachings of U.S. Pat. No. 4,489,268 may result in an AA or AAA battery which is either not within industry standards or which delivers a lesser amount of energy.